1. Field of the Invention
This invention relates generally to submersible artificial lift devices, and in particular to a single or multi-device system provided with a barrier to deter an ingress of well fluids into the device to reduce or prevent development of corrosion, formation of scale or asphaltenes or other problems in an idle device within a wellbore.
2. Background
Submersible artificial lift devices are widely used to pump fluid from a wellbore, particularly for purposes of hydrocarbon recovery. Examples of submersible artificial lift devices include an electrical submersible well pump (ESP) and an electrical submersible progressing cavity pump (ESPCP). Typically, an artificial lift device is suspended within a well from a flow conduit. The artificial lift device is submerged in well fluids. Prolonged inactivity and exposure to well fluids may damage motor and pump components of a typical artificial lift device. Therefore, it is desirable to protect the internals of an inactive artificial lift device when the device is submerged in wellbore fluids.
For example, U.S. Pat. No. 2,783,400 to Arutunoff teaches a protecting unit for an oil field submergible electrical motor. The protective unit provides a pathway for a lubricating and protecting fluid to expand or contract as a result of heating or cooling due to the electric motor. Additionally, the protecting unit essentially doubles the length of a path traveled by moisture or any contaminating fluid before such fluid can reach the pumping unit. One potential drawback of the protecting unit of Arutunoff is that the lengthened moisture path delays rather than prevents moisture migration to the pumping unit.
In some cases, it has been desirable to deploy multiple pumping units within a wellbore. Examples of multiple pumping units include the following:
U.S. Pat. No. 3,741,298 to Canton teaches a multiple well pump assembly wherein upper and lower pumps are both housed in a single wellbore hole and the pumps are connected in parallel so as to supplement each other's output. The pumps may be provided with different flow capacities and may couple with power means for running each pump individually or both simultaneously to provide a well pump system capable of selectively delivering three different effective flow rates from a single wellbore hole to satisfy varying flow demands.
U.S. Pat. Nos. 4,934,458 and 5,099,920 to Warburton et al. teach a small diameter dual pump pollutant recovery system. The system includes a water pump assembly and a pollutant pump assembly mounted at the lower end of piping, which serves to suspend the pumps in a well and also as an exhaust conduit for transporting pump water to the surface. The pollutant pump is used to recover lower density immiscible pollutants from the surface of the underground water table using the cone of the pressure method. The water pump may be raised and lowered to the position at the pollutant/water interface. A method of relocating the pollution intake and resetting the height of the cone of depression when conditions vary the height of the pollutant/water interface is also disclosed.
U.S. Pat. No. 5,404,943 to Strawn teaches a multiple pump assembly for wells. Strawn teaches a design to allow multiple submersible pumps in a single borehole. The multiple pump assembly provides flexibility in use of multiple pumps by allowing the user to avoid multiple well requirements through the use of standby or peak loading pumps.
U.S. Pat. No. 6,119,780 to Christmas teaches a wellbore fluid recovery system and method for recovering fluid from a wellbore that has at least one lateral wellbore extending out therefrom. The system includes a first electrical submergible pumping system for recovering fluids from a first zone of a wellbore and a second electrical submergible pumping system for recovering fluids from a second zone of a wellbore, such as a from a lateral wellbore. The fluid recovery system allows fluid recovery from each lateral wellbore to be independently controlled and also to provide adequate draw down pressure for each lateral wellbore.
U.S. Pat. No. 6,250,390 to Narvaez et al. teaches a dual electric submergible pumping system for producing fluids from separate reservoirs. A first submergible pumping system is suspended from deployment tubing and a second submergible pumping system is suspended from deployment tubing. The first submergible pumping system is connected to a fluid transport such that fluid may be discharged into the first fluid flow path, and a second submergible pumping system is connected to the fluid transport such that the fluid may be discharged into the second fluid flow path.
Typically, once an ESP is located below the static fluid level during deployment of the ESP into the well, wellbore fluid is free to enter into and fill the pump. If a blanking plug is installed, e.g. in a Y-Tool crossover, wellbore fluid is free to fill the open path in the pump and compress the air cap in the pump having a blanking plug in place. Depending on submergence pressure, the wellbore fluid may partially or substantially fully fill the pump.
A difficulty with having an idle unit that is at least partially filled with well fluid is that the idle unit is subject to the possibility of degradation of internal components including scale or asphaltenes precipitating out in the unit, which can cause either plugging of flow passageways and/or interference or locking of rotating components. Therefore, it is desirable to provide a protective environment for internals of the pump(s) that are held in backup or that have a delayed start-up. A protective environment increases the reliability of starting and running the pumps.